Abstract: One or several factors play the main role in low-resistivity reservoirs in different region. But it is hard to analyse. By researching the characters of low-resistivity oil reservoirs in Zhanhua Sag, Shengli Oil Field, China, the main factors of formation of them can determined by analysing such aspect as characters of reservoirs, salinity in strata and drilling engineering. And we suggest it is an effective method by synthetically analyzing the borehole log data, hydrocarbon showing and other geological data to identify reservoirs.